Lower extremity endoskeletal and exoskeletal prostheses, those prosthetic limb systems that are used to replace an amputated portion of a leg and to help restore the amputee's ability to use that leg, are commonly grouped into two categories; above-knee and below knee devices. Both of these types of lower extremity prosthetic limb systems are made to attach to the distal end of an amputated limb and will often include a roll-on suspension sleeve, which attaches directly to the limb, a prosthetic limb socket, which is mechanically or magnetically attached to the suspension sleeve and a prosthetic structural system, which is mechanically attached to a prosthetic coupling mechanism formed within the prosthetic limb socket.
An important consideration in the design of lower extremity prosthetic systems is the strength of the prosthetic socket design and coupling system since the socket is the load-bearing interface between the residual limb and the load bearing prosthetic structural system. Other important considerations are the simplicity of the design and the method of fabrication of the prosthetic socket, as each prosthetic socket must be custom fit to an individual.
Fabrication of lower extremity prostheses typically begins with the making of a positive model of the residual limb or stump. This may be accomplished by a variety of methods, the most common encompasses wrapping the limb with plaster-of-Paris bandages, allowing the bandages to dry thereby creating a negative mold and then filling the negative mold with a mixture of plaster-of-Paris and water and allowing it to harden. Other, more advanced methods for creating positive residual limb models include the use of computer-aided-design (CAD) and computer-aided-manufacturing (CAM) systems with three-dimensional printers. The positive model may then be modified in a number of ways by a skilled prosthetist to accommodate for various weight-bearing and non-weight-bearing surfaces.
Using the modified positive model an intimate fitting prosthetic socket may be formed by means of thermo-molding or thermosetting techniques. During fabrication of the prosthetic socket, an attachment plate or similar coupling device is usually formed within an end of the prosthetic socket, which allows a prosthetic structural system to be bolted or otherwise connected to the prosthetic socket. A variety of prior art attachment plates (e.g. Grace Plate) are available, the most common of which include a standard four hole pattern (e.g., the Otto-Bock European pattern or the USMC pattern).
Another important goal when making a prosthetic socket is that the coupling device most be properly positioned with respect to the positive model in order to fit and function properly. With prior art prosthetic systems this goal is often difficult to achieve. For example, one common prior art coupling system employs a three-prong adapter mechanism for positioning the coupling device on the positive model. This system requires that the three prongs be bent and shaped to the contours of a positive model. Because the three prongs do not create an intimate contact with the positive model a resin material is added to the coupling device to make up this space. After the resin hardens the three-prong adapter may not be repositioned, if it is later determined that the coupling device is not properly aligned with the positive model. Still other systems require that the positive model be reshaped so that an attachment plate will be at a correct degree.
As a convenience in locating the attachment plate holes after the prosthetic socket is formed, cap head screws are typically placed in the holes. After fabrication of the socket, the thermo-molded or thermoset material will be higher over the screw heads than in surrounding areas and may be ground away to expose the screw heads. The screws may then be removed with an Allen Wrench exposing the plate holes. Even with the use of the cap head screws, finishing the end of the socket can be very time consuming.
Other systems, such as the Becker Orthopedic Model 403000 Plate, which incorporates a knurled surface, eliminate the need to vacuum form plastic on the underside of the attachment plate. Although these attachment plates reduce the time and effort required to finish the plate they employ a fingertip type grip between the plate and the laminated material, which is a substantially weaker bond than the above-described fabrication methods.
These and other prior art systems are effective in attaching a lower extremity prosthetic limb system to an amputated limb, however, because each prosthetic socket must be custom designed to an individual, these systems can be difficult and time-consuming to manufacture. Therefore, it is desirable to have a prosthetic limb system that is more quickly and easily fabricated without sacrificing the structural integrity of the prosthetic socket. It is also desirable to have a prosthetic limb system that has enhanced structural features and that is easier to attach to an amputated limb.